Dual voltage power system for use with vehicle alternators and the like

ABSTRACT

There is disclosed herein a dual voltage power unit for use in automobiles, campers, and the like for normally supplying the relatively low DC voltage from an alternator to a storage battery and other electrical devices of the vehicle and for supplying a higher voltage, such as 115 volts, for external usage such as for lighting, emergency power, and so forth. Several circuits are disclosed herein for providing a dual output DC voltage, or for providing a low DC voltage and a higher AC voltage at 60 hertz. The system includes a rectifier circuit coupled with the output of an alternator for normally providing the usual automotive DC voltage, such as 14.5 volts. A load sensor and control circuit are provided for sensing the demand for the higher voltage and for controlling rectifier circuits to supply the same.

United States Patent Peck [541 DUAL VOLTAGE POWER SYSTEM FOR USE WITHVEHICLE ALTERNATORS AND THE LIKE [72] Inventor: Donald W. Peck, NewburyPark, Calif. [73] Assignee: Oaks Power Corporation [22] Filed: Sept. 15,1970 211 Appl. No.: 72,311

[52] U.S. Cl. ..322/28, 290/40, 307/10 R, 307/28, 307/47, 307/75, 321/28[51] Int. Cl. .LH02p I00 [58] Field of Search 90/40; 307/9, 10, 22, 26,307/28, 29, 47, 59, 75; 321/28; 322/14, 15, 28

[56] References Cited UNITED STATES PATENTS Teter A/ reeA/Aroe June6,1972

Primary Examiner-William M. Shoop, Jr. Attorney-Lyon & Lyon ABSTRACTThere is disclosed herein a dual voltage power unit for use inautomobiles, campers, and the like for normally supplying the relativelylow DC voltage from an alternator to a storage battery and otherelectrical devices of the vehicle and for supplying a higher voltage,such as l 15 volts, for external usage such as for lighting, emergencypower, and so forth. Several circuits are disclosed herein for providinga dual output DC voltage, or for providing a low DC voltage and a higherAC voltage at 60 hertz. The system includes a rectifier circuitcoupled-with the output of an alternator for normally providing theusual automotive DC voltage,such as 14.5 volts. A load sensor andcontrol circuit are provided for sensing the demand for the highervoltage and for controlling rectifier circuits to supply the same.

12 Claims, 3 Drawing Figures PATENTEDJUH 61972 3,668,514

SHEET 80F 2 49. a ATTGZ/WEVS DUAL VOLTAGE POWER SYSTEM FOR USE WITHVEHICLE ALTERNATORS AND THE LIKE This invention relates to power unitsand more particularly to dual voltage power units or power supplies forsupplying different output voltages upon demand.

l-leretofore systems have been proposed for providing from thealternator of. a vehicle a dual voltage output. However, such systemshave been characterized by relatively complex circuitry and the like,lack of reliability, and so forth. In particular, such devices have beenconstructed wherein the output of the usual alternator-rectifier isdisconnected from the battery circuit through the use of a relay orsilicon controlled rectifier (SCR) circuit. As is known, a positivevoltage on the gate of an SCR causes the same to conduct regardless ofwhether or not this positive voltage is subsequently removed. in orderto turn off the SCR, the source voltage must be reduced or the currentacross the SCR must be reduced for a predetermined period of time, suchas several microseconds. Usually, a capacitor and switch are employedacross the source to drop the supply current to the SCR for a suflicientperiod of time so as to turn off the SCR. Frequently the switch used isa relay or another SCR. However, such control circuits for SCRs arecharacterized by noise problems, which tend to turn the SCR back onafter it has been turned off, and the usual switch contact problemsassociated with switch-capacitor control arrangements. The presentconcepts obviate these disadvantages of prior art control circuits whilestill providing a relatively simple dual voltage supply which isreliable in operation.

Accordingly, it is a principal object of the present invention toprovide a novel dual voltage power unit.

Another object of this-invention is to provide an improved controlcircuit for silicon controlled rectifiers and the like.

A further object of this invention is to provide a dual voltage supplyfor use with an alternator in providing low and high DC output voltages.

Another object of this invention is to provide a novel dual voltagepower supply for use with an alternator for providing a low DC outputand a higher AC output.

These and other objects and features of the present invention willbecome better understood through a consideration of the followingdescription taken in conjunction with the drawings in which:

FIG. la is a circuit diagram of a system in accordance with theteachings of the present invention for providing a dual DC voltageoutput;

FIG. lb illustrates a modification for a portion of the circuit of HG.1a; and

FIG. 2 is a block diagram of a dual voltage power unit according to thepresent concepts for providing DC and AC output voltages. 4

Briefly, in accordance with an exemplary embodiment of the concepts ofthe present invention, a suitable dual voltage output is provided byemploying three conventional silicon controlled rectifiers and threeconventional rectifiers coupled with a three-phase alternator, such asthose employed in automobiles and other vehicles. These rectifierssupply the normal battery charging and vehicle accessory equipmentvoltage. Additionally, a plurality of diodes are employed for supplyingan external higher voltage, such as l to 1 volts DC. A load sensor isprovided, and upon demand for the higher external voltage, the throttleof the vehicle is automatically set at a predetermined position to causethe alternator to run at a speed so as to provide a sufficient poweroutput. The load sensor also causes the SCRs to turn off. Several of theother diodes then supply the higher voltage to an external power plug.Thus, the SCRs normally supply the usual approximately 14.5 volts DC,but are turned off upon demand for external power and then voltage issupplied through other diodes to the external plug. An alternativearrangement for accomplishing a similar objective is disclosed, andanother alternative arrangement is disclosed for providing an AC outputto the external power plug.

Turning now to the drawings, and first to FIG. la, an exemplary systemis illustrated including an alternator 10 coupled though a controlcircuit 1 1, including three silicon controlled rectifiers 12 through14, to a vehicle battery 15. Positive rectifiers 16 and negativerectifiers 17 are connected with the output of the alternator 10. Thenegative rectifiers 17 are connected to ground at 18, and the positiverectifiers are connected to a power plug 19 and to a voltage regulator20. A load sensor 21 is coupled between the power plug 19 and thecontrol circuit 11 for controlling the operation of the control circuit1 l in response to'demand for power at the power plug. A throttlesolenoid 22 also is coupled with the load sensor.

Before turning to a detailed description of the circuit in FIG. 1a, ageneral discussion of the operation will be set forth. The alternator 10is rotated by the engine of the vehicle, and is excited by the vehiclebattery 15 through the voltage regulator 20 in a conventional manner.The alternating current output of the alternator 10 is rectified by abridge rectifier system including the negative rectifiers 17, positiverectifiers 16, and the SCRs 12 through 14in the control circuit 11. Thepositive rectifiers l6 furnish the positive high voltage, such as 1 l0volts DC, to the power plug 19; whereas the SCRs 12 through 14 furnishcurrent to the battery 15 when turned on. When an external load isplugged into the power plug 19, the load sensor 21 detects the currentdrawn and turns off the SCRs 12 through 14 thereby disconnecting theoutput of the alternator 10 from the vehicle battery 15. The load sensor21 also applies current to the throttle solenoid 22 to increase thespeed of the engine of the vehicle to a predetermined point. The voltageof the battery 15 drops allowing the voltage regulator 20 to feed fullbattery voltage to the field of the alternator 10 in a conventionalmanner. This increases the alternator voltage output, and when thisvoltage reaches the desired high voltage, such as to l 15 volts DC, thevoltage regulator 20 reduces the alternator field voltage to regulatethe output at the desired high voltage. When the external load is turnedoff or disconnected, the load sensor 21 removes current from thesolenoid 22 allowing the engine to return to idle, and turns on the SCRs12 through 14 thereby connecting the output of the alternator back tothe battery 15. The voltage regulator 20 then regulates the alternatoroutput for a bettery input voltage of approximately 14.5 volts DC in aconventional manner.

Turning more specifically to the circuit shown in FIG. 1a, thealternator 10 includes conventional stator windings 2 6 and a rotorwinding 27. The stator windings are connected through lines 28 through30 to the anodes of the SCRs 12 through 14, the cathodes of which are inturn connected together and to an output low voltage line 31. This line31 is connected to the positive terminal of the battery 15, the negativeterminal of which is grounded at 18. The negative rectifiers, which maybe silicon diodes, are connected from the alternator output lines 28through 30 to ground 18. Similarly, the positive rectifiers 16, whichalso may be silicon diodes, are connected from the output lines 28through 30 to a line 33 which is connected to a positive terminal 34 ofthe power plug 19. The negative terminal 35 of the power plug isconnected through a diode 36 to ground 18. The line 33 also is coupledthrough a voltage dropping resistor 37 to the control input of thevoltage regulator 20, the field output of which is connected by a line38 to the rotor 27 of the alternator 10. The line 33 from the positiverectifiers 16 also is coupled through resistors 40 through 41 to therespective gates of the SCRs 12 through 14. These gates also are coupledthrough respective diodes 43 through 45 to a line 46 which is connectedto the output of the load sensor 21.

A line 48 is connected from the power plug terminal 35 to the input ofthe load sensor 21. The load sensor 21 includes input load resistors 49and 50 coupled with the base of a transistor 51. The emitter of thistransistor is grounded at 18, and the collector thereof is coupledthrough a coupling resistor 52 to the base of a transistor 53. Thecollector of this transistor is coupled through the throttle solenoid 22to ground at 18, and a load resistor 54 is coupled between the emitterof this transistor and the collector of the transistor 51.

The emitter of the transistor 53 is connected to the output line 46. Anemitter diode 56 is connected between the emitter of the transistor 53and the line 31.

Turning more specifically to the operation of the circuit of FIG. 1a,during operation, the silicon controlled rectifiers 12 through 14 areturned on to furnish current through the line 31 to the battery 15 asnoted earlier. The voltage regulator is set in a conventional manner toregulate the output of the alternator for a system voltage ofapproximately 14.5 volts DC. This voltage also appears across theterminals 34 and 35 of the power plug 19.

When a load is applied to the power plug 19, the load sensor 21 detectsthe load and causes the SCRs 12 through 14 to turn 011'. This allows thebattery voltage to drop to approximately 12.6 volts, and the voltageregulator 20 senses this voltage drop and increases the voltage on thealternator field. When the outputvoltage on the line 33 reaches thedesired value of 1 10 to 1 volts, current through the voltage droppingresistor 37 is fed to the voltage regulator input to cause it toregulate the alternator output at 1 10 to l 15 volts. The load sensoralso causes the throttle solenoid 22 to advance the vehicle throttle toincrease the speed of the engine to a predetermined point so that thealternator will furnish the desired power to the power plug.

Although shown separately, the load sensor 21 may be con sidered toinclude the high current diode 36 which is connected between thenegative terminal 35 of the power plug 19 and ground 18. When the loadis applied to the power plug 19 as noted earlier, the voltage dropacross the diode 36 is applied across the load resistor 50 and throughthe resistor 49 to the base of the transistor sl. This causes thetransistor 51 to conduct thereby dropping the collector voltage thereofto a low value and causes current to be drawn through the load resistor54 and coupling resistor 52. The current through the coupling resistor52 appears at the base of the transistor 53. The emitter of thetransistor 53 acts as an emitter follower and through the diodes 43through 45 causes a reduction in the gate voltage of the respective SCRs12 through 14 to a negative value with respect to their cathodes therebyturning ofi the SCRs. Collector current of the transistor 53 passesthrough the emitter diode 56 and through the throttle solenoid in thecollector circuit thereof. This causes the throttle solenoid to actuate,thereby advancing the engine throttle.

The diodes 16 rectify the output of the alternator l0 and apply thisoutput through the line 33 to the power plug 19 as noted earlier. Thisoutput is also applied through the resistors v 40 through 42 to thegates of the SCRs 12 through 14. This arrangement, during low voltageoperation, turns on the SCRs 12 through 14, which furnish thelow voltageDC output on.

the voltage regulator in a conventional manner as indicated by a dashedline'58. This voltage is fed through a diode 59 to the voltage sensingcoil 60 of the voltage regulator, and through normally closed relaycontacts 61-62 to the field output line 38. When the ignition voltagereaches approximately 14.5 to 15 volts, the relay contacts 61-62 openplacing a resistor 63 in series with the field output. This reduces thealter nator output voltage which reduces the battery and ignitionvoltage causing the contacts 61-62 to again close and apply full currentto the alternator field. This increases the alternator voltage and thiscycle repeats. The result is a regulated output voltage of approximately14.5 'volts. When the SCRs 12 through 14 are turned off, the loweredbattery voltage allows the regulator contacts 61-62 to close therebyincreasing the alternator output until the current through the voltagedropping resistor 37 causes the voltage regulator relay to operate. Thevalue of the resistor 37 is chosen so that the operating point of thevoltage regulator is reached when the high voltage output isapproximately 1 10 to l 15 volts.

in the manner described previously.

Turning again to the control of the SCRs 12 through 14, the

same are operated by changing the voltage on the output line 46 of theload sensor 21. Considering one SCR 12, for example, the same is inseries with alternator output line 28 and line 31. The diode 43 iscoupled between the gate of the SCR 12 and the line 46 which may beconsidered a control point. Because the source is AC, the SCR l2automatically goes on and off because the source voltage varies frompositive to negative. However, the load sensor 21 and diode 43 allow theSCR 12 to be intentionally turned off by supplying a negative voltage tothe control point or line 46. The SCRs 13 and 14 operate in a likemanner.

FIG. lb illustrates a portion of a circuit constituting a modificationof the circuit of FIG. In. Similar componentsare designated by likereference numerals. Thus, the SCRs 12 through 14 are connected fromrespective output lines 28 through 30 of the alternator 10 to a line 31which in turn is connected to the battery 15. Similarly, the line 33from the positive rectifiers 16 is connected to the positive terminal ofv 65 and the resistors 40 through 42 to the gates of the SCRs l2 through14 to cause the SCRs to turn on, thereby supplying the alternator outputto the battery 15. When the battery is fully charged, the currentthrough a diode 68 causes the voltage regulator to regulate the outputvoltage of the alternator When a load is applied to the power plug 19,the voltage drop across input resistor 50 of the load sensor 21 islimited to approximately +0.75 volt by the diode 36. This voltage is fedthrough the resistor 49 to the base of transistor 51 which causes thistransistor to conduct thereby lowering the voltage at the resistor 70 tonear ground. The current through the resistor 70 causes the base of thetransistor 53 to go negative which causes this transistor to conduct.Collector current of the transistor 53 flows through the throttle coil22 and causes the engine to speed up as noted earlier. The emittervoltage of the transistor 53 is maintained at approximately +12 volts bythe diode 56 which is coupled with the positive terminal of the battery15. The emitter current of the transistor 53 and diode 56 removesthe-positive voltage from the gates of the SCRs 12 through 14 therebyturning off these rectifiers. This disconnects the output of thealternator from the battery 15 thereby lowering the voltage through thediode 68 causing the voltage regulator to increase the alternator outputvoltage. When the rectified output across the power plug 19 reaches 1 10to volts, the current through the resistor 37 causes the voltageregulator to regulate this output voltage.

When the load is removed from the power plug 19, the positive voltage atthe base of the transistor 51 is removed which removes the negativevoltage at the base of the transistor 53, thereby turning off thesolenoid 22 allowing the engine to slow down to an idle. The reductionof emitter current of the transistor 53 allows the voltage at theterminal 66 to increase which in turn allows the SCRs 12 through 14 toagain turn on and apply current to the line 31.

Turning now to the embodiment of FIG. 2, the same illustrates anarrangement utilizing the foregoing concepts, but for providing a low DCvoltage output and a high AC voltage output, such as 1 10 volts Ac at 60hertz. In this case, the alternator 10 is controlled by the voltageregulator 20 as described earlier. The alternating current output of thealternator 10 is three-phase and usually between 300 and 600 hertz. Twosets of bridge rectifiers are used in this instance, with rectifiers 16Aand 17A providing a positive or one halfwave output, and rectifiers 16Band 17B providing a negative or other half-wave output. A hertzoscillator 80 is coupled with a flip-flop 81 to cause the flip-flop tochange state at a 60 hertz rate. The flip-flop 81 alternately turns onand off a positive keyer 82 and negative keyer 83. These keyersalternately turn on and off the respective rectifiers l6A-17A and16B-l7B, respectively,

causing the output voltage thereof to go positive and negative at a 60hertz rate. 7

When the load is removed from the output plug 19, the load sensor 84stops the oscillator 80, and causes the flip-flop 81 to maintain thepositive keyer 82 on and the negative keyer 83 ofi. The load sensor alsocauses acontrol switch 85 to turn on connecting the now positivealternator output on output line 86 to the vehicle battery, and removescurrent from the throttle solenoid 22 allowing the engine speed torettunto an idle. The voltage regulator 20 now regulates the alternator fieldto maintain the battery voltage at 14.5 volts in a manner like thatdescribed earlier.

When a load is again applied to the power plug 19, the load sensor 84turns ofi the control switch 85, turns on the oscillator 80 therebyallowing the flip-flop 81 to operate as described earlier. Likewise, thethrottle solenoid 22 is turned on to increase the engine speed toapredetemiined point, and the voltage regulator 20 regulates the outputof the alternator at the higher voltage.

The present embodiments of this invention are to be considered in allrespects as illustrative and not restrictive, the scope of the inventionbeing indicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims therefore are intended to be embraced therein.

What is claimed is: 1. A power system for use with vehicle altematorsand the like for providing a first voltage output and a second highervoltage output, comprising rectifier means adapted to be coupled with avehicle alter,- nator for supplying first and second rectified voltageoutputs, said rectifier means comprising a first group of rectifier forrectifying the alternator output voltage and providing said firstrectified voltage output for normal vehicle usage, and a second group ofrectifiers for rectifying the alternator output voltage and providingsaid second rectified voltage output of higher voltage than said firstrectified voltage output 1 load-sensor means coupled with said rectifiermeans and responsive to a demand for said higher voltage for causingsaid rectifier means to supply said higher voltage,

plug means coupled between said rectifier means and said load sensormeans for receiving said higher voltage, and voltage regulator meansresponsive to said first and second rectified outputs and adapted to becoupled to said alternator for regulating the output of said alternator.

2. A system as in claim 1 including,

throttle solenoid means adapted to be coupled with the throttle of avehicle for controlling the engine speed thereof, said throttle solenoidmeans being coupled with and responsive to said load sensor means.

3. A system as in claim 1 wherein,

said first group of rectifiers comprises silicon controlled rectifiershaving their anode-cathode circuit coupled to supply said firstrectified voltage output and having gate electrodes, said load sensorbeing coupled to said gate electrodes of said silicon controlledrectifiers.

4. A system as in claim 3 including,

rectifier means coupled between the load sensor means and said gates ofsaid silicon controlled rectifiers, and

said load sensor means comprises switching means responsive to thedemand for said higher voltage for lowering the voltage applied to saidgates.

5. A system as in claim 3 including,

throttle solenoid means adapted to be coupled to control the enginespeed of a vehicle, said throttle solenoid means being coupled to andresponsive to said load sensor means.

6. A system as in claim 1 wherein said first group of rectifierscomprises a plurality of silicon controlled rectifiers having theiranode-cathode circuits coupled to supply said first rectified voltageoutput and having gate electrodes,

impedance means coupled with the second group of rectifiers forsupplying said second rectified voltage output to the gates of saidsilicon controlled rectifiers for nonnally causing said siliconcontrolled rectifiers to supply said first rectified voltage output, and

means coupling said gates to the output of said load sensor means forcausing said silicon controlled rectifiers to turn off upon demand forsaid higher voltage.

7. A system as in claim 6 wherein said impedance means comprises aplurality of resistances having first temiinals respectively coupledwith said gates and second terminals connected to a common terminal, andmeans coupling said common terminal to the output of said first group ofrectifiers, and

said means coupling the output of said load sensor means to said gatescomprises a plurality of rectifiers having first terminals respectivelycoupled with said gates and second terminals coupled with the output ofsaid load sensor means.

8. A system as in claim 1 wherein said first group of rectifierscomprises a plurality of silicon controlled rectifiers having theiranode-cathode circuits coupled to supply said first rectified voltageoutput and having gate electrodes,

means coupled between said second group of recti-fiers and said gatescomprising a plurality of resistances having first terminalsrespectively coupled to said gates and second terminals connected to acommon tenninal, and a resistance coupled between said common terminaland the output of said second group of rectifiers, and

means coupling the output of said load sensor means with said commonterminal.

9. A system as in claim 1 wherein said second rectified output is amodulated alternating current output, and including oscillator controlmeans coupled to said rectifier means for causing said rectifier meansto provide alternating current output upon demand therefor.

10. A power system for use with vehicle altemators and the like forproviding a first voltage output for vehicle usage and a second highervoltage output; comprising rectifier means adapted to be coupled with avehicle alternator for rectifying the alternator output and supplyingfirst and second rectified voltage outputs, said rectifier meanscomprising a first group of rectifiers including silicon controlledrectifiers having their anode-cathode circuit coupled to supply saidfirst rectified voltage output and having gate electrodes, andcomprising a second group of rectifiers for supplying said secondrectified voltage output of higher voltage than said first rectifiedvoltage output,

plug means coupled with the output of said second group of rectifiersfor receiving said higher voltage,

load sensor means coupled with said plug means and to said first groupof rectifiers for causing said higher voltage to be supplied to saidplug means upon demand at said plug means for said higher voltage, saidload sensor means including switching means for causing a reduction ofthe voltage on said gates of said silicon controlled rectifiers, and

impedance means coupling the output of said load sensor means with saidgates of said silicon controlled rectifiers and including rectifiermeans coupling said output of said load sensor means with the output ofsaid first group of rectifiers.

11. A power system for use with vehicle altemators and the like forproviding a first voltage output and a second higher voltage outputcomprising rectifier means adapted to be coupled with a vehiclealternator for receiving the alternator output and supplying first andsecond voltage outputs, said first voltage output being a substantiallylow level DC output and said second voltage output being a substantiallyhigher alternating voltage output, said rectifier means comprising afirst providing a control signal and oscillator means responsive to saidload sensor means coupled with said rectifier means. 12. In a dualvoltage power supply system for use with a .vehicle alternator forproviding a first out-put voltage and a second higher output voltageiheimprovement comprising silicon controlled rectifier means having ananode-cathode circuit coupled to receive an alternating voltage andprovide a first output voltage to a load, said rectifier means includinga control gate,

means coupling said gate to receive said alternating voltage,

output circuit means to which said second higher voltage is supplied,

switching means coupled with said output circuit means and responsive todemand for said second higher voltage for reducing the voltage on saidgate to turn off said silicon controlled rectifier means, and 1 meanscoupling said switching means to said gate.

' m a: a n a

1. A power system for use with vehicle alternators and the like forproviding a first voltage output and a second higher voltage output,comprising rectifier means adapted to be coupled with a vehiclealternator for supplying first and second rectified voltage outputs,said rectifier means comprising a first group of rectifier forrectifying the alternator output voltage and providing said firstrectified voltage output for normal vehicle usage, and a second group ofrectifiers for rectifying the alternator output voltage and providingsaid second rectified voltage output of higher voltage than said firstrectified voltage output load sensor means coupled with said rectifiermeans and responsive to a demand for said higher voltage for causingsaid rectifier means to supply said higher voltage, plug means coupledbetween said rectifier means and said load sensor means for receivingsaid higher voltage, and voltage regulator means responsive to saidfirst and second rectified outputs and adapted to be coupled to saidalternator for regulating the output of said alternator.
 2. A system asin claim 1 including, throttle solenoid means adapted to be coupled withthe throttle of a vehicle for controlling the engine speed thereof, saidthrottle solenoid means being coupled with and responsive to said loadsensor means.
 3. A system as in claim 1 wherein, said first group ofrectifiers comprises silicon controlled rectifiers having theiranode-cathode circuit coupled to supply said first rectified voltageoutput and having gate electrodes, said load sensor being coupled tosaid gate electrodes of said silicon controlled rectifiers.
 4. A systemas in claim 3 including, rectifier means coupled between the load sensormeans and said gates of said silicon controlled rectifiers, and saidload sensor means comprises switching means responsive to the demand forsaid higher voltage for lowering the voltage applied to said gates.
 5. Asystem as in claim 3 including, throttle solenoid means adapted to becoupled to control the engine speed of a vehicle, said throttle solenoidmeans being coupled to and responsive to said load sensor means.
 6. Asystem as in claim 1 wherein said first group of rectifiers comprises aplurality of silicon controlled rectifiers having their anode-cathodecircuits coupled to supply said first rectified voltage output andhaving gate electrodes, impedance means coupled with the second group ofrectifiers for supplying said second rectified voltage output to thegates of said silicon controlled rectifiers for normally causing saidsilicon controlled rectifiers to supply said first rectified voltageoutput, and means coupling said gates to the output of said load sensormeans for causing said silicon controlled rectifiers to turn off upondemand for said higher voltage.
 7. A system as in claim 6 wherein saidimpedance means comprises a plurality of resistances having firstterminals respectively coupled with said gates and second terminalsconnected to a common terminal, and means coupling said common terminalto the output of said first group of rectifiers, and said means couplingthe output of said load sensor mEans to said gates comprises a pluralityof rectifiers having first terminals respectively coupled with saidgates and second terminals coupled with the output of said load sensormeans.
 8. A system as in claim 1 wherein said first group of rectifierscomprises a plurality of silicon controlled rectifiers having theiranode-cathode circuits coupled to supply said first rectified voltageoutput and having gate electrodes, means coupled between said secondgroup of recti-fiers and said gates comprising a plurality ofresistances having first terminals respectively coupled to said gatesand second terminals connected to a common terminal, and a resistancecoupled between said common terminal and the output of said second groupof rectifiers, and means coupling the output of said load sensor meanswith said common terminal.
 9. A system as in claim 1 wherein said secondrectified output is a modulated alternating current output, andincluding oscillator control means coupled to said rectifier means forcausing said rectifier means to provide alternating current output upondemand therefor.
 10. A power system for use with vehicle alternators andthe like for providing a first voltage output for vehicle usage and asecond higher voltage output, comprising rectifier means adapted to becoupled with a vehicle alternator for rectifying the alternator outputand supplying first and second rectified voltage outputs, said rectifiermeans comprising a first group of rectifiers including siliconcontrolled rectifiers having their anode-cathode circuit coupled tosupply said first rectified voltage output and having gate electrodes,and comprising a second group of rectifiers for supplying said secondrectified voltage output of higher voltage than said first rectifiedvoltage output, plug means coupled with the output of said second groupof rectifiers for receiving said higher voltage, load sensor meanscoupled with said plug means and to said first group of rectifiers forcausing said higher voltage to be supplied to said plug means upondemand at said plug means for said higher voltage, said load sensormeans including switching means for causing a reduction of the voltageon said gates of said silicon controlled rectifiers, and impedance meanscoupling the output of said load sensor means with said gates of saidsilicon controlled rectifiers and including rectifier means couplingsaid output of said load sensor means with the output of said firstgroup of rectifiers.
 11. A power system for use with vehicle alternatorsand the like for providing a first voltage output and a second highervoltage output comprising rectifier means adapted to be coupled with avehicle alternator for receiving the alternator output and supplyingfirst and second voltage outputs, said first voltage output being asubstantially low level DC output and said second voltage output being asubstantially higher alternating voltage output, said rectifier meanscomprising a first group of rectifiers for providing said first voltageoutput for normal vehicle useage, and a second group of rectifiers forproviding said second higher voltage output, plug means coupled withsaid rectifier means for receiving said higher voltage output upondemand therefor, and control means coupled between said plug means andsaid rectifier means for causing said higher voltage output to besupplied from said rectifier means upon demand at said plug meanstherefor, said control means including load sensor means coupled withsaid plug means for providing a control signal and oscillator meansresponsive to said load sensor means coupled with said rectifier means.12. In a dual voltage power supply system for use with a vehiclealternator for providing a first out-put voltage and a second higheroutput voltage, the improvement comprising silicon controlled rectifiermeans having an anode-cathode circuit coupled to receive an alternatingvoltage and provide a first output voltage to a load, said rectifiermeans including a control gate, means coupling said gate to receive saidalternating voltage, output circuit means to which said second highervoltage is supplied, switching means coupled with said output circuitmeans and responsive to demand for said second higher voltage forreducing the voltage on said gate to turn off said silicon controlledrectifier means, and means coupling said switching means to said gate.